Event Driven RRM (ED-RRM) is a feature that allows an AP in distress to bypass normal RRM intervals and immediately change channels.

A CleanAir AP is always monitoring AQ, and reports on this in 15 second intervals. AirQuality is a better metric than relying on normal Wi-Fi chip noise measurements because AirQuality only reports on Classified Interference devices. This makes AirQuality a reliable metric because it is known what is reported is not because of Wi-Fi energy (and hence not a transient normal spike).

Before configuring ED-RRM you have to enable Clean Air functionality on the WLC. You can do this under ” Wireless -> 802.11a/n or 802.11b/g/n -> Clean Air” section as shown below. You can customize sources of interference, AQI trap threshold, enable interference traps, etc.

If you want to enable this feature on specific AP, you can do that as well. You can do this via “Wireless -> Access Points-> Radio -> 802.11a/n or 802.11b/g/n ” section by selecting the required AP. This setting will override the global band settings.

For ED-RRM a channel change only occurs if the Air Quality is sufficiently impacted. Because Air Quality can only be affected by a classified known to CleanAir non- Wi-Fi source of interference (or an adjacent overlapping Wi-Fi channel), the impact is understood:

1. Not a Wi-Fi anomaly
2. A crisis condition at this AP

Crisis means that CCA is blocked. No clients or the AP can use the current channel. Under these conditions RRM would change the channel on the next DCA pass. However, that could be a few minutes away (up to ten minutes depending on when the last run was performed), or the user could have changed the default interval and it could be longer (selected an anchor time and interval for longer DCA operation). ED-RRM reacts very quickly (30 seconds) so the users that change with the AP are likely unaware of the crisis that was close. 30 -50 seconds is not long enough to call a help desk. The users that do not are in no worse shape than they would have been in the first place.

In all cases the interference source was identified and the AP change reason logs that source, and the users that have poor roaming receives an answer as to why this change was made. The channel change is not random. It is picked based on device contention, thus it is an intelligent alternate choice.

Once the channel is changed there is protection against triggering ED-RRM again in a hold down timer (60 seconds). The event channel is also marked in RRM DCA for the affected AP to prevent a return to the event channel (3 hours) in the event the interferer is an intermittent event and DCA does not see it immediately. In all cases the impact of the channel change is isolated to the affected AP.

Suppose a hacker or someone of ill intent fires up a 2.4 GHz jammer and all channels are blocked. First off, all the users within the radius are out of business anyway. However, suppose ED-RRM triggers on the all APs that can see it. All APs change channels once, then hold for 60 seconds. The condition would be met again, so another change would fire with the condition still being met after 60 seconds. There would be no channels left to change to and ED-RRM activity would stop. A security alert would fire off on the jammer (default action) and you would need to provide a location (if with MSE) or nearest detecting AP. ED-RRM would log a major AQ event for all affected channels. The reason would be RF jammer. The event would be contained within the effected RF domain and well alerted.

You can enable ED-RRM under “Wireless-> {802.11a/n|802.11b/n} -> RRM -> DCA” section as shown below. There are 3 sensitivity level of Air Quality threshold which could trigger ED-RRM. By default it is set to Medium ( which is AQ of 50). You can set it either High Sensitivity ( AQ of 60) or Low sensitivity (AQ of 35).

Persistent Device Avoidance is another mitigation feature that is only possible with CleanAir APs. A device that operates periodically, such as a microwave oven, can introduce destructive levels of interference while it is operating. However, once it is no longer in use the air goes quiet again. Devices such as video cameras, outdoor bridge equipment, and microwave ovens are all examples of a type of device called persistent.

These devices can operate continuously or periodically, but what they all have in common is that they do not move frequently. RRM of course sees levels of RF noise on a given channel. If the device is operating long enough RRM even moves an active AP off the channel that has interference. However, once the device goes quiet, it is likely that the original channel presents as the better choice once again. Because each CleanAir AP is a spectrum sensor the center of the interference source can be evaluated and located. Also, you can understand which APs are affected by a device that you know is there, and potentially operates and disrupts the network when it does. Persistent Device Avoidance allows us to log the existence of such interference and remember that it is there so you do not place an AP back on the same channel. Once a Persistent Device has been identified it is “remembered” for seven days. If it is not seen again then it is cleared from the system. Each time you see it, the clock starts over.

You can configure this setting on the same section “Wireless -> 802.11 -> RRM -> DCA ” section as shown below.

You can monitor Clean Air in “Monitor -> Cisco CleanAir” section in each band. Normally you would see 80.211b/g/n with lower AQI due to large number of devices operate in that band & always congested.

Here is the Cisco Clean Air Design Guide (Doc ID 112139) used as reference for this. You can read this for complete understanding of this feature & how you can configure WCS/MSE for reporting on your wireless network.